Although conventional film-screen X-ray radiography has been successfully used for nearly a century, it still has many deficiencies. The exposure range of the film screen system is limited so that the film can be over- or under-exposed. The exposure display latitude and the contrast of the film are also limited. The film requires wet chemical processing. Not only is chemical processing inconvenient, it also delays access to the image.
Digital radiography provides a solution to the problems of conventional radiography. The useful exposure display latitude attainable from digital image receptors is often superior to film, because the variable window level and contrast display of digital images eliminate the display limitations of the film. Because the image is acquired in digital form, it can be enhanced by software manipulation, readily transferred to remote locations for analysis, and easily stored in digital form. No wet chemical processing is required.
Systems have been developed to capture patterns of X-rays using solid state components, generally using X-ray sensitive phosphors, intensifiers or photoconductive materials, and arrays of microelectronic devices to convert X-ray patterns to electrical signals. These systems involve converting an X-ray image pattern into an array of electrical signals, which are subsequently used to produce a visible display of the X-ray image. Such systems are described in, for example: Jeromin, U.S. Pat. No. 5,168,160; Lee, U.S. Pat. No. 5,319,206; Lee, U.S. Pat. No. 5,331,179; Jeromin, U.S. Pat. No. 5,381,014; Lee, U.S. Pat. No. 5,563,421; Lee, U.S. Pat. No. 5,648,660; and Lee, U.S. Pat. No. 5,652,430; all of which are incorporated herein by reference.
An important consideration in such systems is the signal to noise ratio of the system. As the signal to noise ratio is increased, sharper images can be produced and/or patient dose can be reduced. Thus, there is a continuing need for image capture elements that have an improved signal to noise ratio.